Microlepidogaster discus Martins, Rosa & Langeani, sp. nov.

Microlepidogaster discus Martins, Rosa & Langeani, sp. nov.

(Fig. 1; Tabs. 1–2)

Type material. Holotype. DZSJRP 19101, male, 46.4 mm SL, Brazil, Minas Gerais State, Botumirim, unnamed stream on dirt road Itacambira-Botumirim, tributary to rio Itacambiruçu, rio Jequitinhonha basin, 16°47’40”S 43°03’39”W, 946 m asl., 23 Sep 2013, F. Langeani, F. R. Carvalho, B. N. Andrade, A. C. Rosa.

Paratypes. All from Brazil, Minas Gerais State. DZSJRP 19112, 13, 11.4–39.7 mm SL, Josenópolis, unnamed stream downstream city, on dirt road from Grão Mogol to Josenópolis, tributary to rio Itacambiruçu, rio Jequitinhonha basin, 16°32’45”S 42º31’41”W, 24 Sep 2013, F. Langeani, F. R. Carvalho, B. N. Andrade, A. C. Rosa. DZSJRP 19493, 18 (2 c&s), 31.9–45.4 mm SL; MCP 48182, 2, 38.7–41.1 mm SL; MZUSP 115384, 2, 38.6–41.0 mm SL, collected with holotype.

Diagnosis. Microlepidogaster discus can be distinguished from all congeners by having the ventral laminar expansions of cleithrum and coracoid bearing only 1–30 odontodes restricted to the area near the pectoral-fin insertion (vs. 50–120 odontodes, generally more than 100, extending to the middle portion of pectoral girdle); the anterior plates of mid-ventral lateral series reduced, not ventrally elongated, the first or the second markedly round (Fig. 2) (vs. anterior plates of mid-ventral lateral series large, curved and elongated, similar to most of the other anterior plates of the series; fig. 3a in Schaefer, 1997); pectoral-fin unbranched ray distinctly divided distally, with 7–15 ossified segments reaching almost half of its length (Fig. 3) (vs. ossified segments absent, or when present less than seven, restricted to the tip of the ray); and accessory process on first epibranchial present (Fig. 4) (vs. absent). Additionally, M. discus can be distinguished from all congeners, except for M. dimorpha, by having the anterior portion of compound supraneural plus first dorsal-fin proximal radial contacting the neural spine of the seventh vertebra (vs. eighth or ninth vertebra in M. perforatus, ninth vertebra in M. arachas, and 10th or 11th vertebra in M. longicolla). Also, the new species differs from M. perforatus and M. dimorpha by having pointed odontodes at the anterior portion of rostral plates (vs. rounded leaf-shaped odontodes). Microlepidogaster discus is also distinguished from M. longicolla and M. perforatus by having the mid-dorsal lateral series of plates surpassing the vertical through dorsal-fin length (vs. mid-dorsal lateral series reduced, reaching the vertical through dorsal-fin base, and never surpassing the dorsal-fin length). Finally, it also differs from M. perforatus by having the median series of lateral plates complete, reaching the end of the caudal peduncle (vs. median series of lateral plates terminating two plates before the end of the caudal peduncle); and by the possession of an iris operculum (vs. iris operculum absent).

Description. Morphometric and meristic data in Tables 1 and 2. Dorsal body profile slightly convex from tip of snout to tip of parietosupraoccipital; almost straight to caudal-fin origin. Ventral body profile almost straight from tip of snout to pelvic-fin origin; ascending from pelvic-fin origin to end of anal-fin base; straight to caudal-fin origin. Greatest body depth variable, at parietosupraoccipital tip or at dorsal-fin origin. Greatest body width at posterior margin of opercle, gradually tapering towards snout and caudal fin. Caudal peduncle ellipsoid in transverse section, slightly flattened dorsally and ventrally. Head shallow; longitudinal crest and hypertrophied odontodes absent. Anterior margin of snout rounded in dorsal view; tip of snout with variable coverage, with many small irregular-shaped plates, frequently with naked area in its most anterior portion, more evident in juveniles; anterior odontodes small and pointed, similar in size to other on remainder head and body. Lateral plate series with subequal-sized odontodes randomly distributed. Odontodes of head and body not forming conspicuous rows. Eye small, dorsolaterally placed, not visible from below. Iris operculum present. Compound pterotic quadrangular in shape, its posterior extension poorly-developed, far from rib of sixth vertebra; compound pterotic fenestrae most irregular in shape and variable in size, small in dorsal and large in ventral portion of bone. Infraorbital canal entering infraorbital series via sphenotic. Parietosupraoccipital not contributing to dorsal wall of swimbladder capsule.

Body entirely covered by dermal plates, except on ventral part of head, region overlying opening of swimbladder capsule, around pelvic-fin origin, and region in front of urogenital opening. Abdomen entirely covered with small-sized plates randomly distributed.

Lips roundish, papillose; lower lip larger than upper lip, almost reaching pectoral girdle; papillae gradually smaller toward lip edges. Maxillary barbel reduced, free from oral disk. Teeth slender and bifid; median cusp larger and rounded, lateral smaller and pointed. Premaxillary teeth 17–29 (21). Dentary teeth 15–27 (21).

Dorsal-fin rays ii,7; originating approximately at vertical through end of pelvic-fin base; tip of adpressed rays almost reaching vertical through end of anal-fin base; spinelet small, somewhat elliptical in shape, locking mechanism non-functional. Anterior portion of compound supraneural plus first dorsal-fin proximal radial contacting neural spine of seventh vertebra. Pectoral-fin rays i,6; originating immediately behind opercular opening; tip of adpressed rays reaching vertical through end of pelvic-fin base. Pectoral-fin unbranched ray distinctly divided distally, with 7–15 segments reaching almost half of its length. Exposition of cleithrum and coracoid lateral, restricted to area near pectoral-fin insertion, with few odontodes (1–30), remaining portions of pectoral girdle covered by skin. Arrector fossa partially enclosed by ventral laminar expansions of coracoid and cleithrum, opening very ample, extending laterally towards pectoral-fin base; opening region not covered with plates. Pectoral axillary slit present only in juveniles; some adults with vestigial round pore. Pelvic-fin rays i,5; unbranched ray shorter than branched rays. Anal-fin rays i,5. Caudal-fin rays i,14–15 (14),i; concave; lower lobe slightly longer than upper lobe; 3–5 (4) dorsal and 2–4 (3) ventral procurrent rays. Adipose fin absent; one or two azygous, round or elongate, plates in place of adipose fin present in some specimens.

Mid-dorsal series of lateral plates surpassing vertical through dorsal-fin length. Median lateral plate series 27–32 (29); complete from compound pterotic to caudal-fin base. Anterior plates of mid-ventral lateral series reduced, not ventrally elongated; first or second markedly round. Vertebrae 31.

Color in alcohol. Ground color of head and body light-brown to medium-brown on dorsal region and lightbrown on lateral and ventral areas. Head dark brown along parietosupraoccipital. Dark brown lateral stripe inconspicuous in most specimens, one and half lateral plate deep, from anterior portion of snout to caudal peduncle end, joining dark brown blotch at base of branched caudal-fin rays. Four dorsal dark brown saddles, more conspicuous in melanic specimens, extending lateroventrally and fused to lateral stripe: first starting little ahead and extending along first third of dorsal-fin base, second from very end of dorsal-fin base extending along three posterior mid-dorsal lateral plates, third after vertical line passing through end of anal-fin base, and fourth at end of caudal peduncle. Large specimens, including holotype, with round spots, smaller than orbital diameter, below lateral stripe and ventral surface of body. All fins, except for caudal, with hyaline membranes and medium to dark brown, small, and elongate blotches along rays. Caudal-fin color pattern variable, most specimens with two transverse dark brown bars, first at base and second subterminal; some specimens with last one divided in two transverse bars.

Sexual dimorphism. Males with a conspicuous urogenital papilla immediately posterior to anus (vs. absent in females); an expanded flap of skin on the dorsal surface of the first pelvic-fin ray, also present on branched rays, though less developed (vs. absent in females); and tip of adpressed pelvic fin reaching or surpassing anal-fin origin (vs. tip of adpressed pelvic fin not reaching anal-fin origin in females). Dissected female with approximately 70 large oocytes asynchronically developed.

Distribution. Microlepidogaster discus is only known from headwaters of the rio Itacambiruçu, an affluent on the left side of the rio Jequitinhonha, a coastal basin in southeastern Brazil (Fig. 5).

Behavioral notes. Handling specimens during sampling caused them to fold their lips longitudinally, partially or totally, with right and left halves, including the barbels, contacting at midline (Fig. 6). The function of this behavior is unknown.

Etymology. The specific epithet is from the Latin discus, meaning flat circular plate, in reference to the first reduced and round plates in the mid-ventral lateral series, a diagnostic feature of the species. A noun in apposition.